CN104126000A - Improvements relating to pressure compressor lubrication - Google Patents

Abstract

A lubricant composition for lubricating a high pressure compressor, the composition comprising a Fischer-Tropsch derived base oil and a polymeric thickener. Use in high pressure compressors, especially hyper compressors is described, as are high pressure olefin methods.

Description

Improvement of High Pressure Compressor Lubrication

field of invention

The present invention relates to lubricants for high pressure compressors, especially ultra high pressure compressors. In particular, although not exclusively, the present invention relates to lubricants for high pressure compressors comprising polymeric thickeners.

Background of the invention

In the manufacture of high-pressure polyolefins, such as high-pressure low-density polyethylene (HP-LDPE) or ethylene-vinyl acetate (EVA), high operating pressures of 70-350 megapascals (MPa, or about 10,000-50,000 psi) are typical Yes, an operating pressure of 240-310 MPa (about 35,000-45,000 psi) is preferred. To achieve these high pressures, one or more high pressure compressors, including ultra high pressure compressors (or two stage compressors) are employed.

To make high pressure polyolefins, typically the olefinic feedstock (eg ethylene) is first compressed by one or more primary high pressure compressors to pressures up to about 25-30 MPa. Thereafter, one or more ultra-high pressure compressors are employed to achieve the typically required high operating pressures, followed by conversion of the olefinic feedstock to polyolefins (eg HP-LPDE) in the reactor in the presence of a catalyst. The remaining unpolymerized feedstock can be recycled for recompression.

The term "high pressure compressor" is used herein to mean any compressor capable of compressing feedstock, preferably ethylene, to a pressure of at least 20 MPa, preferably at least 30 MPa, when the manufacture of high pressure polyolefins is particularly relevant to the present invention. The term "ultrahigh pressure compressor" is used herein to refer to any compressor capable of compressing feedstock, preferably ethylene, to a pressure of at least 50 MPa, preferably at least 100 MPa, either as a primary compressor or preferably as a secondary compressor.

Typical operating pressures in the manufacture of high pressure polyolefins, especially HP-LDPE, are one of the highest, if not the highest, of any industrial process. High-pressure compressors, in particular ultrahigh-pressure compressors, are therefore based on a special construction. They typically contain moving parts made of extremely hard materials such as tungsten carbide.

The operation of high pressure compressors, including ultra high pressure compressors, requires the use of lubricants to reduce friction between moving parts such as plunger/piston and cylinder. Lubricants for high-pressure compressors, especially ultra-high pressure compressors, have special requirements in view of the high operating pressures and the construction of high-pressure compressors, especially ultra-high pressure compressors. One of the most difficult challenges for equipment lubricants is posed by the type of ultra-high pressure compressors typically used to manufacture high pressure polyolefins, especially polyethylene.

For example, it is known that lubricants used in ultra-high pressure compressors inevitably leak downstream into the polymerization reactor, mixing with and becoming part of the reaction materials such as ethylene, comonomer, solvent, catalyst, etc. This, in turn, can interfere with the formation of high pressure polyolefins or lead to degradation of polyolefin properties; hence lubricants with low contamination impact are desired.

Mineral oils have traditionally been used as high-pressure and ultra-high-pressure compressor lubricants, and even if they leak into the reaction mass, they are not suitable for the formation of high-pressure polyolefins or the use of polyolefins in subsequent manufacturing processes such as molding or extrusion. There are few adverse effects. However, mineral oil alone is not an effective high pressure compressor lubricant, which typically degrades rapidly due to dissolution of the compressed material in the compressor. Such dissolution is a unique challenge in formulating lubricants for high pressure, especially ultra-high pressure compressors, while ensuring that the lubricant remains pumpable (ie, has the proper viscosity).

One prior art approach has used, for example, polyglycols with low solubility in ethylene as lubricants in ultra-high pressure compressors. WO2009012041 describes ultra-high pressure compressor lubricants comprising polyether diols having no more than one hydroxyl functionality.

Another prior art approach has been to add thickeners such as polybutene to mineral oil ultra high pressure compressor lubricants, as disclosed for example in US5578557.

It is an object of the present invention to provide lubricant compositions for high-pressure compressors, especially ultrahigh-pressure compressors, having improved resistance to dissolution, especially resistance to olefin dissolution, and good viscosity/pumpability.

Summary of the invention

In a first aspect, the present invention is a lubricant composition for lubricating a high pressure compressor, the composition comprising a Fischer-Tropsch derived base oil and a polymeric thickener.

It has been surprisingly found that Fischer-Tropsch derived base oils are less prone to thickening with polymeric thickeners such as polybutene than mineral base oils. This may represent a disadvantage of Fischer-Tropsch derived base oils in most lubricant applications, but the inventors have exploited this reduced thickening to achieve a significant advantage in lubricating high pressure compressors, especially ultra high pressure compressors. The inventors have found that at a given viscosity, eg a targeted pumping viscosity, a greater weight proportion of polymeric thickener can be incorporated into a Fischer-Tropsch derived base oil than into a mineral base oil. In the specific field of high-pressure compressors, the presence of a higher proportion of polymeric thickeners is advantageous, helping to increase resistance to dissolution in compressed feedstocks such as ethylene at high pressure, minimizing the decrease in viscosity and thus helping Resists lubricant degradation. This is achieved without trade-off of increased viscosity: Fischer-Tropsch based lubricant compositions of the present invention were found to outperform comparable mineral oil compositions at a given weight ratio of polymeric thickener incorporated. In contrast, exhibits a reduced viscosity (see examples). In other words, less Fischer-Tropsch base oil may be required to bring a given amount of polymeric thickener into an ultra-high pressure compressor without changing other properties of the lubricant such as kinematic viscosity at 40 and 100°C .

According to a second aspect, the invention comprises the use of a lubricant composition comprising a Fischer-Tropsch derived base oil and a polymeric thickener for lubricating high pressure compressors. For example, according to a third aspect, the invention includes a method of lubricating a high pressure compressor comprising applying a lubricant composition comprising a Fischer-Tropsch derived base oil and a polymeric thickener to one or more of the high pressure compressors. on the friction interface. According to a fourth aspect, the present invention also includes a high pressure compressor lubrication kit comprising: a lubricant composition comprising a Fischer-Tropsch derived base oil and a polymeric thickener; and applying the lubricant composition to high pressure compression machine instructions.

In a fifth aspect, the present invention is directed to a method of pressurizing an olefin, the method comprising: introducing an olefin into a high pressure compressor lubricated by a lubricant composition comprising a Fischer-Tropsch derived base oil and a polymeric thickener; and using the A high pressure compressor pressurizes the olefin.

In a sixth aspect, the present invention is directed to a process for the manufacture of high pressure polyolefins, the process comprising: pressurizing the olefin with a high pressure compressor lubricated with a lubricant composition comprising a Fischer-Tropsch derived base oil and a polymeric thickener; and The pressurized olefins are reacted to form high pressure polyolefins.

In a seventh aspect, the present invention relates to the use of a Fischer-Tropsch derived oil as a base oil in a high pressure compressor lubricant composition comprising a polymeric thickener. For example, according to an eighth aspect, the invention includes a method of making a high pressure compressor lubricant composition comprising mixing a Fischer-Tropsch derived base oil with a polymeric thickener.

In a ninth aspect, the present invention relates to the use of a Fischer-Tropsch derived oil as a base oil in a lubricant composition comprising a polymeric thickener, thereby achieving a higher operating efficiency than is achieved with a comparable application of a mineral oil. The weight percent content of the thickener in the composition.

In a tenth aspect, the present invention relates to the use of a Fischer-Tropsch derived oil as a base oil in a lubricant composition comprising a polymeric thickener, thereby achieving a lower operating ratio than that achieved for a comparable application of a mineral oil. Viscosity in the composition.

Preferred features and embodiments of the invention are set forth in the following detailed description, which may be combined with each other and with all aspects of the invention where the context permits.

Detailed description of the invention

The first essential ingredient in the lubricant composition herein is a Fischer-Tropsch derived base oil. As used herein, the term "Fischer-Tropsch derived" means that the material is or is derived from a synthesis product of a Fischer-Tropsch condensation process. Fischer-Tropsch derived base oils may also be referred to as "GTL (Gas to Liquids)" base oils.

The Fischer-Tropsch condensation process is the conversion of carbon monoxide and hydrogen into long-chain hydrocarbons, usually paraffins; in the presence of a suitable catalyst and typically at elevated temperatures (eg 125-300°C, preferably 175-250°C) And/or under pressure (eg 5-100 bar, preferably 12-50 bar), n(CO+2H ₂ )=(-CH ₂ -)n+nH ₂ O+heat. Hydrogen:carbon monoxide ratios other than 2:1 can be used if desired.

The carbon monoxide and hydrogen themselves may originate from organic or inorganic, natural or synthetic sources, typically from natural gas or organically sourced methane. Gases typically converted to liquid fuel components by the Fischer-Tropsch process may include natural gas (methane), LPG (e.g. propane or butane), "condensates" such as ethane, synthesis gas (CO/hydrogen) and those derived from coal, Gaseous products of biomass and other hydrocarbons.

The Fischer-Tropsch process can be used to produce a variety of hydrocarbon fuels, including LPG, naphtha, kerosene and gas oil fractions. Of these, gas oils have been used as and in automotive diesel fuel compositions, typically in blends with petroleum derived gas oils. The heavy fractions, typically after hydrotreating and vacuum distillation, can produce a range of base oils with different distillation properties and viscosities, which can be used as lubricating base oil stocks.

The hydrocarbon product may be obtained directly from the Fischer-Tropsch reaction, or indirectly, for example by fractional distillation of the Fischer-Tropsch synthesis product or from a hydrotreated Fischer-Tropsch synthesis product. Hydrotreating may include hydrocracking to adjust the boiling range and/or hydroisomerization which may improve cold flow properties by increasing the proportion of branched paraffins. Other post-synthetic treatments such as polymerization, alkylation, distillation, cracking-decarboxylation, isomerization and hydroreforming can be used to modify the properties of the Fischer-Tropsch condensation product.

Typical catalysts for the Fischer-Tropsch synthesis of paraffins comprise, as catalytically active constituents, metals of Group VIII of the Periodic Table of the Elements, in particular ruthenium, iron, cobalt or nickel. Suitable catalysts of this type are described, for example, in EP-A-0583836 (pages 3 and 4).

An example of the Fischer-Torkey process is the SMDS (Shell Middle Distillate Synthesis Process) described in the paper "The Shell Middle Distillate Synthesis Process" published by van der Burgt et al at the Fifth Synfuels Worldwide Symposium, Washington DC, November 1985. ); see also the publication of the same name by Shell International Petroleum Company Ltd, London, UK, November 1989. The process (also sometimes referred to as Shell's "gas-to-liquids" or "GTL" technology) produces products in the middle distillate range by converting synthesis gas derived from natural gas (mainly methane) into heavy long-chain hydrocarbons (paraffins) Waxes that can then be hydroconverted and fractionated to produce liquid transportation fuels such as gas oils that can be used in diesel fuel compositions. Base oils, including heavy base oils, can also be produced from such processes.

By the Fischer-Tropsch process, the Fischer-Tropsch derived base oil is substantially free of sulfur and nitrogen, or has an undetectable content of sulfur and nitrogen, eg, less than 5 ppm. Compounds containing these heteroatoms tend to behave as poisons for Fischer-Tropsch catalysts and are therefore removed from the syngas feed. This can bring additional benefits to the lubricant compositions of the present invention. Furthermore, the normally operated Fischer-Tropsch process produces little or no aromatic components. The aromatics content of the Fischer-Tropsch derived base oil component is typically less than 1 wt%, preferably less than 0.5 wt%, more preferably less than 0.1 wt%, on a molecular (rather than atomic) basis, suitably determined according to ASTM D-4629 .

In general, Fischer-Tropsch derived hydrocarbon products have a relatively low content of polar components, especially polar surfactants, eg compared to petroleum derived hydrocarbons. These polar components may include, for example, oxygen-containing compounds and sulfur- and nitrogen-containing compounds. Low sulfur content in Fischer-Tropsch derived hydrocarbons is usually indicative of low oxygenate and nitrogen content since they are all removed by the same treatment process.

In one embodiment, a Fischer-Tropsch derived base oil is defined as having a paraffin content greater than 80 wt% paraffins, preferably greater than 85 wt% or even greater than 90 wt% paraffins and a saturate content greater than 99 wt%, and comprises a range of Isoparaffins of n+1, n+2, n+3 and n+4 carbon atoms, where n is 20-35. The presence of this continuous series of isoparaffins can be determined by field desorption/field ionization (FD/FI) techniques. In this technique, an oil sample is first separated into a polar (aromatic) phase and a non-polar (saturate) phase by utilizing high performance liquid chromatography (HPLC) method IP368/01, where pentane is used instead of the method specified Hexane was used as mobile phase. Saturates and aromatic fractions were then analyzed with a Finnigan MAT90 mass spectrometer equipped with a field desorption/field ionization (FD/FI) interface, where FI ("soft" ionization technique) was used to identify hydrocarbon species by carbon number and hydrogen deficiency. Classification of compounds in mass spectrometry is determined by the characteristic ions formed and is usually classified by "z-value". This is given by the general formula C _n H _2n+z for all hydrocarbon species. Since the saturate phase is analyzed separately from the aromatic phase, the content of different isoparaffins with the same stoichiometry or n value can be determined. The mass spectrometer results were processed using commercial software (poly32 from Sierra Analytics LLC, 3453 Dragoo Park Drive, Modesto, California GA 95350 USA) to determine the relative proportion of each hydrocarbon species.

The Fischer-Tropsch derived base oil used in the present invention may preferably have a kinematic viscosity at 100°C according to ASTM D445 of at least 2 mm ² /s, more preferably at least 4 mm ² /s, most preferably at least 7 mm ² /s. The Fischer-Tropsch derived base oil may preferably have a kinematic viscosity at 100°C of at most 50 mm ² /s, more preferably at most 35 mm ² /s, most preferably at most 25 mm ² /s.

The Fischer-Tropsch derived base oil for use in the present invention is preferably obtained by (1) a Fischer-Tropsch synthesis step, (2) a (partial) Fischer-Tropsch synthesis product hydrocracking/hydroisomerization step , preferably followed by (3) a pour point depressing step of (a fraction of) the product of the hydrotreating step. Solvent dewaxing or catalytic dewaxing can achieve the lowering of the pour point in step (3). The desired base oil with the desired viscosity can be isolated from the dewaxed product by means of distillation. The oil is optionally hydrorefined or subjected to an adsorption treatment in order to improve its color.

To obtain Fischer-Tropsch derived oils, a Fischer-Tropsch synthesis step can be performed, for example, according to the so-called commercial Sasol process, the commercial Shell Middle Distillate Process or the non-commercial Exxon process. These and other processes are described in detail in EP-A-776959, EP-A-668342, US-A-4943672, US-A-5059299, WO-A-9934917 and WO-A-9920720. Most of these publications also describe the above-mentioned hydroisomerization/hydrocracking step (2).

Suitable Fischer-Tropsch derived base oils which may suitably be used as base oils in the lubricant compositions of the present invention are, for example, described in EP0776959, EP0668342, WO97/21788, WO00/15736, WO00/14188, WO00/14187, WO00/14183 , WO00/14179, WO00/08115, WO99/41332, EP1029029, WO01/18156 and WO01/57166.

In order to ensure the purity of the high-pressure polyolefin, the base oil used in the present invention may preferably be a Fischer-Tropsch derived white oil meeting one or more relevant standards.

The white oil may be technical grade white oil, and may preferably meet relevant statutory standards, such as those defined by FDA 21 CFR 178.3620(b). Technical grade white oils may have a Cybolt color of at least +20. The extreme value of UV absorbance per cm optical path length can be a maximum of 4.0 at 280-289nm, a maximum of 3.3 at 290-299nm, a maximum of 2.3 at 300-329nm, and a maximum of 0.8 at 330-350nm.

In order to facilitate the use of high pressure polyolefin articles in food applications, it is preferred that the base oil is, for example, a Fischer-Tropsch derived medical grade white oil complying with one or more of the following: EU Directive on plastic materials and articles intended to come into contact with food 2002/72/EEC, European Pharmacopoeia 5th Edition, US Pharmacopoeia 25th Edition/NF20, FDA21CFR172.878, FDA21CFR178.3620(a) and FDA21CFR178.3570(USDA H-1).

Preferably, the medical grade white oil should contain no more than 5% (w/w) mineral hydrocarbons with a carbon number less than 25, have a kinematic viscosity at 100°C according to ASTM D445 of at least 7 mm ² /s and even 8.5 mm ² /s, and The average molecular weight is at least 480 g/mol.

In one embodiment, the Fischer-Tropsch derived white oil may have a Cybot color greater than +25 and preferably equal to +30. The content of polar compounds is preferably less than 1 wt%, and the content of acyclic isoparaffins is preferably 75-98 wt%. According to FDA178.3620(c), the ultraviolet (UV) absorption spectrum value measured in accordance with ASTMD2269 is preferably less than 0.70 in the 280-289nm spectral band, less than 0.60 in the 290-299nm spectral band, less than 0.40 in the 300-329nm spectral band, and less than 0.40 in the 330-289nm spectral band. The 380nm spectral band is less than 0.09. The pour point of the oil is preferably below -10°C, more preferably below -15°C. The CN value measured according to IEC590 is preferably less than 30, more preferably 15-30.

Suitable Fischer-Tropsch derived white oils may for example be produced according to the process of WO02070627A2 which allows the production of base oils having kinematic viscosities at 100°C of about 2-30 cSt suitable for process oil applications or as medical grade white oils.

Another example of a Fischer-Tropsch derived medical grade white oil is found in WO2009018087.

In order to improve the color properties of the white oil fraction obtained eg from WO02070627A2, a final refining treatment may be performed. Examples of suitable finishing treatments are so-called sulfuric acid treatment processes, hydrofinishing or hydrogenation processes and adsorption processes. Sulfuric acid treatment see for example the general textbook "Lubricant Base Oil and Wax Processing", Avilino Sequeira, Jr, Marcel Dekker Inc., New York, 1994, Chapter 6, pp. 226-227.

The hydrofinishing is suitably carried out at a temperature of 180-380°C, at a total pressure of between 10-250 bar and preferably above 100 bar and more preferably between 120-250 bar. WHSV (Weight Hourly Space Velocity) is 0.3-2 kg oil per liter of catalyst per hour (kg/1·h).

The hydrogenation catalyst is suitably a supported catalyst comprising a dispersed Group VIII metal. Possible Group VIII metals are cobalt, nickel, palladium and platinum. The cobalt and nickel containing catalyst may also contain Group VIB metals, suitably molybdenum and tungsten. Suitable supports or support materials are low acidity amorphous refractory oxides. Examples of suitable amorphous refractory oxides include inorganic oxides such as alumina, silica, titania, zirconia, boria, silica-alumina, fluorinated alumina, fluorinated silica-alumina and mixtures of two or more thereof.

Examples of suitable hydrogenation catalysts are: nickel-molybdenum containing catalysts such as KF-847 and KF-8010 (AKZO Nobel), M-8-24 and M-8-25 (BASF), and C-424, DN- 190, HDS-3 and HDS-4 (Criterion); nickel-tungsten-containing catalysts such as NI-4342 and NI-4352 (Engelhard) and C-454 (Criterion); cobalt-molybdenum-containing catalysts such as KF-330 (AKZO - Nobel), HDS-22 (Criterion) and HPC-601 (Engelhard). Preference is given to using platinum-containing catalysts, more preferably platinum and palladium-containing catalysts. A preferred support for these palladium and/or platinum containing catalysts is amorphous silica-alumina. Examples of suitable silica-alumina supports are disclosed in WO-A-9410263. A preferred catalyst comprises an alloy of palladium and platinum, preferably supported on an amorphous silica-alumina support, commercially available catalyst C-624 from Criterion Catalyst Company (Houston, TX) is an example.

The white oil obtained from the above process including an optional hydrogenation step may also be contacted with an adsorbent to further enhance its color properties. Examples of suitable heterogeneous adsorbents are activated carbon, zeolites such as natural faujasite, or synthetic materials such as ferrierite, ZSM-5, faujasite, mordenite, metal oxides such as silica powder, silica gel, aluminum Oxides and various clays such as Attapulgus earth (hydrous magnesium aluminum silicate), Porocel earth (hydrated alumina). A preferred adsorbent is activated carbon.

Fischer-Tropsch derived base oils may be present in the lubricant compositions herein in an amount of at least 50%, preferably at least 60%, more preferably at least 70%, by weight of the lubricant composition. Fischer-Tropsch derived base oils are preferably present in the lubricant compositions herein in an amount of up to 95%, more preferably up to 90%, still more preferably up to 85% or even up to 80%, by weight of the lubricant composition.

Advantageously, all base oils in the lubricant compositions herein may be Fischer-Tropsch derived. However, in addition to Fischer-Tropsch derived base oils, the lubricant compositions herein may also comprise non-Fischer-Tropsch derived base oils, such as conventional mineral base oils, such as mineral white oils, preferably meeting one or more of the above criteria industrial or medical grade white oil.

The second essential ingredient in the lubricant composition herein is a polymeric thickener. As used herein, the term "polymeric thickener" is intended to include polymers or oligomers suitable for increasing the viscosity of Fischer-Tropsch base oils.

The terms "polymer" and "polymeric" are used herein to include "oligomer" and "oligomeric" where the context permits.

Polymeric thickeners are also commonly referred to as viscosity modifiers and viscosity index improvers, although viscosity index improvement is not necessary for the purposes of the present invention. Many polymeric thickeners are known in the art and the polymeric thickeners herein may comprise a mixture of one or more such polymers.

Known polymeric thickeners include the family of polyalkyl(meth)acrylates, although they typically suffer from low shear stability. The polyalkyl(meth)acrylate may have a number average molecular weight of 10,000-250,000, for example, 20,000-200,000. Polyalkyl(meth)acrylates can be prepared by conventional free radical or anionic polymerization methods.

The polymeric thickeners herein may preferably be olefin polymers, ie homopolymers, copolymers or terpolymers resulting from the polymerization of olefins, preferably C ₂ -C ₁₀ olefins. The C ₂ -C ₁₀ olefins include, for example, ethylene, propylene, 1-butene, isobutene, 2-butene, isoprene, 1-octene and 1-decene. Exemplary (co)polymers include polypropylene, polyisobutylene, ethylene/propylene copolymers, styrene/isoprene copolymers, styrene butadiene copolymers, and 1-butene/isobutylene copolymers, and their mixture. The olefin polymer may preferably be aliphatic. The olefin forming the olefin polymer may preferably have 2 to about 6 carbon atoms per molecule, and may preferably be selected from one or more of ethylene, propylene, butene, and isoprene.

The polymeric thickeners herein typically comprise polymers having a carbon backbone. Advantageously, the polymer may have a carbon backbone with alkyl branches, each branch having an average of not more than 3 carbon atoms. Branching can be determined based on the monomers used to form the polymer or following the techniques described in "High Temperature GPC utilizing Function Specific Detectors" K Tribe, G Saunders, R Meissner, Macromol. Symp. 2006, 236, 228-23.

Preferably, the olefin polymer herein can conform to the following general structure:

m=0 or 1

n=1-about 110

R ¹ -R ⁴ =H or CH ₃

R ⁵ =H, CH ₃ , C ₂ H ₅ or C ₃ H ₇

As polymeric thickeners herein, polybutene-based olefin polymers, especially homopolymers, formed from butene, especially isobutylene, are most preferred. The above general structure is representative of polybutene-like olefins.

Polybutene is commercially available from a number of manufacturers and is typically made via acid-catalyzed cationic polymerization of isobutene-rich C4 streams.

Early polybutene products were made from butene mixtures containing n-butene and isobutene, for example from feeds that were predominantly butadiene raffinate or from fluid catalytic cracking (FCC) processes with 20-40% A crude C4 stream of n-butenes is produced. The polymers produced in these processes are said to contain polybutene and polyisobutene in varying proportions, typically 5-70% polyisobutene and 95-30% poly-n-butene.

While the polybutenes described above are useful as polymeric thickeners herein, subsequent processes have been developed to produce polybutenes that are relatively low in n-butenes, or substantially free of n-butenes. For the purposes of the present invention, by BP chemistry with and Trademarks are sold, now for example under Polymers of this type, commercially available from Ineos Ltd, which are close to pure polyisobutene (PIB), even with some entrained n-butenes, are preferred herein.

One process for obtaining polybutene useful as a thickener for the polymers herein is described in EP-A-0145235, in which a preformed boron trifluoride-ethanol complex is used as the isobutylene polymerization catalyst. The process produces a polymer that is not only low in or substantially free of n-butenes, but also substantially free of chlorine.

In one embodiment, the proportion of n-butene in the polymer backbone defined by the ratio of the polymer's infrared absorption at 740 cm ⁻¹ to 4335 cm ⁻¹ may be less than 0.5, most preferably less than 0.25. The determination of the proportion of n-butene in the polymer backbone is a concept that is difficult to measure quantitatively and is therefore defined by infrared absorption. The technique for determining the proportion of n-butenes is that described in EP 0640680 A1.

The number average molecular weight (M _n ) of olefin polymers, especially polybutenes, for use as polymer thickeners herein may preferably be at least 300, such as at least 600 or 900, most preferably at least 1000. The olefin polymer, especially polybutene, may preferably have a number average molecular weight (M _n ) of at most 10,000, such as at most 6,000 or 2,500, most preferably at most 1,500. Number average molecular weight (M _n ) was determined by gel permeation chromatography, ASTM D3536 (mod) or ASTM D3592 (VPO).

Olefin polymers, especially polybutenes, for use as polymer thickeners herein may preferably have a viscosity at 100°C of at least 10 cSt, such as at least 50 cSt or more preferably 300 cSt, most preferably at least 500 cSt. The olefin polymer, especially polybutene, may preferably have a viscosity at 100°C of at most 100,000 cSt, such as at most 50,000 cSt or 30,000 cSt or 6,000 cSt or 1,000 cSt or most preferably at most 800 cSt. Viscosity at 100°C was measured by ASTM-D-445 standard.

Olefin polymers, especially polybutenes, for use as polymer thickeners herein may preferably have an IUPAC number average degree of polymerization (DP _n ) of at least 3, such as at least 10 or 15, most preferably at least 20. The olefin polymer, especially polybutene, may preferably have an IUPAC number average degree of polymerization (DP _n ) of at most 2000, such as at most 500 or preferably at most 200, most preferably at most 35. The degree of polymerization is defined as the number of monomer units in the number average molecule.

Polymer thickeners may comprise polymer mixtures and thus also extend to several polymers, for example mixtures of several polybutenes, which are synthesized separately and may have molecular weights, viscosities or degrees of polymerization outside the above-mentioned numerical ranges, as long as several It is sufficient that the mixture of polybutenes has a value falling within the above range.

The poly(iso)butenes herein are typically viscous liquids that are miscible with base oils. As mentioned above, it may have a number average molecular weight ( _Mn ) such as 600-10,000, or preferably 1000-1,500, and a 100°C kinematic viscosity such as 50-50000 cSt, or preferably 300-800 cSt.

The polymeric thickener may be present in the lubricant compositions herein in an amount of at least 5%, preferably at least 10%, more preferably at least 15% or even at least 20% by weight of the lubricant composition. The polymeric thickener is preferably present in the lubricant compositions herein in an amount of up to 50%, more preferably up to 40%, still more preferably up to 30%, by weight of the lubricant composition.

Preferably, the lubricant composition of the present invention comprises a Fischer-Tropsch derived base oil and a polymer thickener, wherein the thickener content is 18% by weight based on the total weight of the lubricant composition, and the Fischer-Tropsch derived base oil is ASTM D445 has a kinematic viscosity of at most 10 cSt at 100°C.

Suitably, the lubricant composition of the present invention comprises a mineral base oil and a polymeric thickener, wherein the thickener content is 18% by weight based on the total weight of the lubricant composition, the kinematic viscosity of the mineral base oil at 100°C according to ASTM D445 is at most 12cSt.

In addition, the lubricant composition of the present invention comprises a Fischer-Tropsch derived base oil and a polymer thickener, wherein the thickener content is 25% by weight based on the total weight of the lubricant composition, and the Fischer-Tropsch derived base oil is in accordance with ASTM D445 The kinematic viscosity at 100°C is at least 13 cSt.

Suitably, the lubricant composition of the present invention comprises a mineral base oil and a polymeric thickener, wherein the thickener content is 25% by weight based on the total weight of the lubricant composition, and the kinematic viscosity of the mineral base oil at 100°C according to ASTM D445 for at least 16cSt.

The lubricant compositions of the present invention may contain conventional additives consistent with achieving the desired properties for high pressure compressor applications.

For example, the composition may contain one or more antioxidants. Preferred examples include food-grade oil-soluble hindered phenols and thiophenols, such as hindered phenols such as hindered phenols and bisphenols, hindered 4,4'-thiobisphenols, hindered 4-hydroxy- and 4 -thiol benzoate and dithioate, and hindered bis(4-hydroxy- and 4-thiol benzoate and dithioate) alkylene esters. In one embodiment, the antioxidant is selected from food grade oil soluble aromatic amine antioxidants and is naphthylphenylamine, alkylated phenylnaphthylamine and alkylated diphenylamine. In one embodiment, the composition comprises phenolic and aromatic amine antioxidants in a weight ratio of 20:1 to 1:20. When present, the antioxidant is preferably present in an amount of at most 0.5%, more preferably at most 0.1 wt%.

In one embodiment, the composition comprises 0.05-2.0 wt% of at least one rust inhibitor additive package having a combination of food grade ionic and non-ionic surface active rust inhibiting ingredients. Examples of ionic rust preventive lubricant additives include food grade phosphoric acid, mono and dihexyl ester compounds with tetramethylnonylamine, and mixtures thereof. Examples of non-ionic anti-rust lubricant additives include food grade fatty acids and their esters with sorbitan, glycerol or other polyols or polyalkylene glycols. Other nonionic anti-rust lubricant additives may include food grade ethers from fatty alcohols alkoxylated with oxyalkylenes or sorbitan alkoxylated with oxyalkylenes or sorbitan alkoxylated with oxyalkylenes sugar esters.

In one embodiment, the composition comprises at least one antiwear additive. Examples include, but are not limited to, food-grade oil-soluble sulfur- and/or phosphorus-containing compounds such as triphenylphosphorothioate. Other sulfur and/or phosphorus-containing materials not currently approved for food-grade use include: zinc dialkyldithiophosphates, zinc dithiocarbamate, amine dithiocarbamate, and methylenebisdithioamino Formate.

In one embodiment, the composition further comprises suitable non-toxic emulsifiers. Examples include polyoxypropylene (15) stearyl ether (CFTA name: PPG-15 stearyl ether), ARLAMOL E softener-solvent from ICI Surfactants, U.S.P./N.F. grade emulsifiers such as gum arabic (CAS #9000-01- 5), 2-aminoethanol (CAS#141-43-5), cholesterol (CAS#57-88-5), octadecanoic acid (CAS#57-11-4), lecithin, 9-octadecane Acid (CAS#112-80-1), Polyethylene Glycol-Polypropylene Glycol (CAS#9003-11-6), Polyoxyethylene (20) Cetearyl Ester (CAS#9005-00-9) , Polyoxyethylene (40) Stearate (CAS#9004-99-3), Polysorbate 20 (CAS#9005-64-5), Polysorbate 40 (CAS#9005-66-7) , Polysorbate 60 (CAS#9005-67-8), Polysorbate 80 (CAS#9005-65-8), Sodium Lauryl Sulfate (CAS#151-21-3), Sodium Stearate ( CAS#882-162), sorbitan monooleate (CAS#1338-43-8), sorbitan monopalmitate (CAS#26266-57-9), sorbitan monostearate ( CAS#1338-41-6), Triethanolamine (CAS#102-71-6).

The lubricant composition herein may typically be prepared by simple mixing of its ingredients, preferably at a temperature of at least 50°C, preferably at least 70°C, eg at least 80°C. The mixing temperature, duration and conditions can be appropriately selected by those skilled in the art to achieve uniform dissolution of the polymer thickener or to obtain a transparent and clear composition. In one embodiment, the composition is prepared by heating the base oil to a temperature of at least 80°C, adding the polymeric thickener to the base oil, and stirring for at least 1 hour, preferably 2 hours to achieve uniform dissolution.

According to the present invention, the lubricant compositions herein are used for lubricating high pressure compressors. The use of the lubricant composition in ultra-high pressure compressors is particularly beneficial and is always preferred. Ultra high pressure compressors provide operating pressures of at least 50 MPa, preferably 100 MPa or even 150 MPa, thus requiring lubricants that are particularly resistant to dissolution in compressed feedstocks such as those of the present invention. Therefore, wherever the term "high pressure compressor" is used herein, it also includes the preferred "ultrahigh pressure compressor".

The high-pressure compressor herein may be a horizontal balanced counter-moving reciprocating type. The compressor, especially the ultra-high pressure compressor, may be of positive displacement, reciprocating crosshead, multi-stage type. It may contain one or more sealed plunger cylinders, preferably of commercially available tungsten carbide or tungsten carbide coated steel. The aforementioned compressors are supplied, for example, by Burckhardt Compression AG and NuovoPignone (GE Energy).

According to the invention, the lubricant composition is used to lubricate the frictional interface of a compressor, typically between a moving and a non-moving part of a compressor or between two moving parts. Depending on the application, the lubricant composition may be used for one or more of crankcase lubrication, crosshead lubrication, cylinder lubrication, cooling and flushing. The lubricant compositions herein are particularly useful in cylinder lubrication, which may include the lubrication of one or more of cylinder walls, piston rings, valves, rod pressure packings, and gas seals of high-pressure compressors, or combinations of the lubricants herein applied to it.

To provide the lubricant composition to moving parts, it is typically pumped through one or more passages. For example, cylinders can be lubricated by pressure-feed lubrication. The lower viscosity of the lubricant composition at a given polymeric thickener level is particularly beneficial in this regard because it facilitates pumping and pressure transfer, reducing pumping equipment and energy requirements.

In accordance with the present invention, use of the lubricant composition herein in an ultra-high pressure compressor may comprise supplying the lubricant composition in a kit including instructions for applying the lubricant composition to a high pressure compressor. The instructions may simply take the form of a label identifying the composition as a high pressure compressor lubricant composition or an ultra high pressure compressor lubricant composition. They may be provided, for example, on the container containing the lubricant composition or in accompanying leaflets or documentation. Typically, the instructions in the high pressure compressor lubrication kit may include advice on how to use and apply the lubricant of the present invention, while stating the conditions under which the lubricant may be used such as pressure, preheat and minimum flow.

High pressure compressors can in principle be used to compress any gaseous feedstock, which typically has a low molecular weight (eg below 60, 40 or even 20). The feedstock is typically carbonaceous, ie contains one or more carbon atoms. Particularly common feedstocks are olefins, especially ethylene, which is used in the manufacture of high-pressure low-density polyethylene (HP-LDPE) or ethylene-vinyl acetate.

According to the present invention, the lubricant composition herein may be used in a process for pressurizing or compressing an olefin, the method comprising: introducing the olefin into a high-pressure compressor lubricated by the lubricant composition herein; and compressing the olefin with the high-pressure compressor. pressure. In a preferred embodiment, the olefin is ethylene. The olefin may be pressurized to a pressure of at least 25 MPa, preferably at least 50 MPa, most preferably at least 100 MPa or even 200 MPa.

In accordance with the present invention, the lubricant composition is used in a process for the manufacture of high-pressure polyolefins, the process comprising: pressurizing the olefin with a high-pressure compressor lubricated with the lubricant composition herein; and reacting the pressurized olefin to form a high-pressure polyolefin. olefins. The olefin may preferably be ethylene, and the high pressure polyolefin may be HP-LDPE. Processes and catalysts for producing high pressure polyolefins are known in the art. An example is LyondellBasellLupotech based on high pressure tubular reactors craft. An alternative process uses an autoclave reactor. The invention is not limited as to the exact type of high pressure olefins process, although it is preferred that the olefins are pressurized by a high pressure compressor to a pressure of at least 25 MPa, preferably at least 50 MPa, most preferably at least 100 MPa or even 200 MPa.

As previously stated, the lubricant compositions herein exhibit improved performance over comparable mineral oil-based compositions due to their increased proportion of polymeric thickener.

In view of the particular benefits of combinations of Fischer-Tropsch derived base oils and polymeric thickeners in high pressure compressor lubrication, the present invention includes Fischer-Tropsch derived oils in high pressure compressor lubricant compositions comprising polymeric thickeners Application as base oil.

When used in high pressure compressors, in addition to reducing friction and wear, the lubricant composition acts as a sealing material between moving parts of the compressor, thereby preventing the escape of compressed materials such as ethylene. In this regard, an increased proportion of polymeric thickener in the lubricant composition at a given viscosity is also beneficial.

As will be appreciated by those skilled in the art, mineral or Fischer-Tropsch derived hydrocarbon base oils are soluble in low molecular weight compressed carbonaceous feedstocks such as ethylene in extremely high pressure environments such as high pressure compressors. This in turn means that in high pressure compressor applications, especially ultra-high pressure compressors, the base oil dissolves in the compressed stock and migrates from the lubricated interface, leaving mainly (or only) the polymeric thickener to complete the lubrication and sealed task. Polymeric thickeners do not readily dissolve in low molecular weight compressed materials such as ethylene, thereby maintaining the lubricating and sealing properties of the composition.

In a high pressure compressor environment, it is desirable for the lubricant composition to contain the largest possible proportion of polymeric thickener while remaining pumpable. Since it has been found that the Fischer-Tropsch derived base oils in the lubricant compositions herein allow for the incorporation of greater amounts of polymeric thickeners at a given viscosity compared to mineral base oils, the present invention satisfies the need to provide improved resistance to dissolution, especially Aim for resistance to olefin dissolution as well as good viscosity/pumpability. A greater proportion of the composition enables lubrication in high pressure compressor environments without increasing viscosity.

Fischer-Tropsch derived oils can therefore be advantageously used as base oils in lubricant compositions comprising polymeric thickeners, thereby achieving comparable applications of comparable mineral oils (e.g., mineral oils of the same viscosity) at the same viscosity. A higher percentage by weight of thickener in the composition is achieved. The viscosity may be, for example, the viscosity at 40°C or 100°C at standard temperature and pressure.

Pumpability of the lubricant composition is a particularly important benefit herein. It has been found that the Fischer-Tropsch based lubricant compositions of the present invention exhibit reduced viscosities compared to comparable mineral oil compositions at a given weight ratio of admixed polymeric thickener. This reduced viscosity results in lower necessary pump pressures when delivering the composition to a high pressure compressor. Fischer-Tropsch derived oils can thus be advantageously used as base oils in lubricant compositions comprising polymeric thickeners, thereby achieving what is achieved by comparable applications of comparable mineral oils (e.g. mineral oils of the same viscosity) Lower viscosity in the composition. The viscosity may be, for example, the viscosity at 40°C or 100°C at standard temperature and pressure.

Better pumpability (achieved by lower lubricant viscosity for a given polymer thickener concentration) can offer the advantage of saving energy, or with lubricants containing mineral base oil/polymer thickener combinations In contrast to formulations, it is possible to choose to have a higher polymer thickener concentration in lubricant formulations containing Fischer-Tropsch derived base oils, and to use this higher level of polymer without increasing the viscosity. The thickener is introduced into the ultra-high pressure compressor.

The invention will now be further illustrated by means of non-limiting examples with reference to the accompanying drawings, in which:

Figure 1A shows the 100°C viscosity of an exemplary lubricant composition blend based on a Fischer-Tropsch derived base oil (GTL8) and a mineral base oil (Oil 2), respectively, versus polybutene content at 100°C;

Figure IB shows the 40°C viscosity of an exemplary lubricant composition blend based on a Fischer-Tropsch derived base oil (GTL8) and a mineral base oil (Oil 1), respectively, versus polybutene content at 40°C;

Figure 2 shows the carbon distribution of Fischer-Tropsch derived base oil GTL8.

Example 1

Evaluation of polymer thickener HYVIS Thickening effect of polybutene on isoviscosity base stocks derived from Fischer-Tropsch synthetic or mineral oils.

HYVIS is a product formerly from BP Chemicals Limited. Equivalent products are available from Ineos Ltd under the designation INDOPOL get.

HYVIS The performance of polyisobutene is close to that of polyisobutene, although it typically contains a small amount of n-butene. HYVIS has a molecular weight of about 1300, which can be determined, for example, by ASTM D3592 (VPO) or ASTM D3536 (GPC, modified). HYVIS Other typical physical properties are listed in Table 1.

Table 1

The mineral oil derived base stocks evaluated and compared are:

"GTL8" is a straight run Fischer-Tropsch derived base oil produced by Fischer-Tropsch synthesis followed by hydrocracking, catalytic dewaxing and distillation. The carbon distribution of "GTL8" is shown in Figure 2. GTL8 is industrial grade white oil.

"Oil 1" is a mineral white oil blend with GTL8 isoviscosity at 100°C. The oil was formed by pre-blending 82 wt% Shell Ondina 937 ^™ and 18 wt% Shell Ondina 917 ^™ , both commercial medical grade white oils.

"Oil 2" is a mineral white oil viscous with GTL8 and the like at 40°C. The oil was formed by pre-blending 65 wt% Shell Ondina 937 ^™ and 35 wt% Shell Ondina 917 ^™ , both commercial medical grade white oils.

The properties of the base oils are shown in Table 2.

Table 2

Combine "Oil 1", "Oil 2" and "GTL8" with HYVIS combined to produce HYVIS containing 18wt% and 25wt% (ie, formulations with polybutene treatment ratios of 18 wt% and 25 wt%). In all cases heat the base oil in a beaker to a temperature of 80°C and then add the corresponding amount of HYVIS Stirring for 2 hours in each case resulted in a homogeneous, transparent, clear formulation.

The density, 40°C and 100°C kinematic viscosity and viscosity index (VI) of each formulation thus obtained were measured. Calculation of dynamic viscosity, thickening degree and thickening power of polybutene. The results are listed in Table 3.

Referring to Figure 1B, which illustrates polybutene (HYVIS ) on the comparison of the influence of kinematic viscosity.

Referring to Figure 1A, which illustrates polybutene (HYVIS ) on the comparison of the influence of kinematic viscosity.

A comparison of the kinematic viscosities of formulations derived from isoviscosity base oils (i.e. GTL 8 and oil 1 at 40 °C; GTL 8 and oil 2 at 100 °C) showed that HYVIS Thickening power was reduced in Fischer-Tropsch derived base oils at both 18 and 25% polybutene treat ratios. In other words, formulations based on Fischer-Tropsch derived base oils are less prone to thickening than mineral base oil formulations. The relevant comparisons are as follows:

GTL 8 and oil 1 (18% polybutene treatment ratio, 100°C)

GTL 8 and oil 1 (25% polybutene treatment ratio, 100°C)

GTL 8 and oil 2 (18% polybutene treatment ratio, 40°C)

GTL 8 and oil 2 (25% polybutene treatment ratio, 40°C)

Conversely, the data indicate that a greater weight percent of polybutene can be incorporated into formulations containing Fischer-Tropsch derived base oils at a given viscosity. In other words, to achieve the targeted viscosity, Fischer-Tropsch based formulations require a higher polybutene treat rate than mineral oil based formulations. The term "treatment ratio" refers to concentration.

DISCOVERHYVIS In mineral oil based formulations slightly increased viscosity index (VI), however it was found to slightly decrease viscosity index (VI) in Fischer-Tropsch based formulations.

Despite their increased polymeric thickener content, Compositions 1 and 2 are expected to outperform or match the mineral base oil compositions in the high pressure pumping test due to their high paraffin content.

Compositions 1 and 2 are considered to be particularly suitable as lubricant compositions for high pressure compressors, especially ultra high pressure compressors. The advantageous application of these compositions in high-pressure compressors, especially ultrahigh-pressure compressors, is known.

Claims (15)

CLAIMS 1. Use of a lubricant composition comprising a Fischer-Tropsch derived base oil and a polymeric thickener to lubricate high pressure compressors. 2. The use of claim 1, wherein the high-pressure compressor is an ultrahigh-pressure compressor. 3. The use according to claim 1 or 2, wherein the polymer thickener is a homopolymer, copolymer or terpolymer produced by polymerization of C ₂ -C ₁₀ olefins. 4. Use according to any one of the preceding claims, wherein the polymeric thickener is a homopolymer, copolymer or terpolymer produced by the polymerization of ethylene, propylene, butene or isoprene. 5. Use according to any one of the preceding claims, wherein the polymeric thickener is polybutene. 6. The use of any one of the preceding claims, wherein the polymeric thickener has a number average molecular weight ( _Mn ) of 600-10,000. 7. Use according to any one of the preceding claims, wherein the Fischer-Tropsch derived base oil is a medical grade white oil. 8. Use according to any one of the preceding claims, wherein the Fischer-Tropsch derived base oil has a viscosity of 7 cSt to 50 cSt, preferably 7 cSt to 25 cSt. 9. Use according to claim 1 or 2, wherein the composition comprises 50-95 wt% Fischer-Tropsch derived base oil and 5-50 wt% polymeric thickener. 10. A lubricant composition for lubricating a high pressure compressor comprising a Fischer-Tropsch derived base oil and a polymeric thickener. 11. The lubricant composition of claim 10, comprising 5-50% by weight of a homopolymer, copolymer or polymer produced by the polymerization of ethylene, propylene, butene or isoprene having a number average molecular weight (M _n ) of 600-10,000 Terpolymer as polymer thickener and 50-95 wt% Fischer-Tropsch derived medical grade white oil as base oil. 12. A lubricant composition according to claim 10 or 11 comprising 15-50 wt% polymeric thickener and 50-85 wt% Fischer-Tropsch derived base oil. 13. A high pressure compressor lubrication kit comprising the lubricant composition of any one of claims 10-12 and instructions for applying the lubricant composition to a high pressure compressor. 14. A method of pressurizing an olefin or making a high pressure polyolefin, the method comprising: introducing the olefin into a high pressure compressor lubricated by the lubricant composition of any one of claims 10-12; pressurizing the olefin with the high pressure compressor; and optionally reacting the pressurized olefin to form a high pressure polyolefin. 15. Use of a Fischer-Tropsch derived oil as a base oil in a high pressure compressor lubricant composition comprising a polymeric thickener to achieve: a higher weight percent content of thickener in the composition than would be achieved at the same viscosity with a comparable use of a comparable mineral oil; and/or Lower viscosities in the composition than achievable with comparable use of a comparable mineral oil.